The present invention relates to the provision of a plastics material coating on an optical fiber in general, and more particularly to a method of and apparatus for providing such coating at a high advancement speed on a glass optical fiber.
In the manufacture of glass optical fibers, it is desirable to provide the freshly drawn fiber with a plastics material protective coating as soon as conveniently possible after drawing in order to limit the reduction of strength consequent upon damage to the pristine surface of the optical fiber occasioned by atmospheric attack. This coating is conventionally applied by passing the fiber downwardly through a bath containing a suitable liquid, typically a resin solution or prepolymer. The fiber leaves the bath with a liquid coating which is then cured to form a plastics protective sheath for the fiber. If the fiber is passed too quickly through the coating bath, there arises an increasing tendency for incomplete wetting of the fiber and formation of bubbles in the coating, or more usually for lengths of fiber to emerge entirely unwetted and completely devoid of coating. One approach to ameliorating this problem, which is described in United Kingdom Patent Specification No. 1,441,086, involves placing ballotini in the coating bath to strip bubbles from the fiber. A disadvantage of this approach is the risk of damage to the fiber by the bubble-stripping action of the ballotini.